Knee joint arthroplasty is a common surgical procedure by which a failing natural knee is replaced with a prosthetic knee. The natural knee may fail due to trauma, such as a sports injury or vehicular accident, or due to degenerative disease, such as arthritis.
There are two types of prosthetic knees: a primary knee and a revision knee. Primary knee prostheses are used when failure of the natural knee is not so severe. For example, primary knee prostheses can be used when the ligaments in the natural knee are still intact. Revision knee prostheses are used for more severe failure of the natural knee or failure of a primary knee prosthesis.
In patients who require a revision knee system, there is a lot of bone loss, and therefore, a lack of normal bony reference points, or landmarks, for properly aligning the implant. In these cases, surgeons use the intramedullary canal of the tibia as the landmark for positioning the tibial prosthesis. However, problems arise in positioning the implant because the location of the natural canal varies among individuals. For example, if the tibial stem of the implant is not properly aligned with respect to the intramedullary canal in the medial/lateral direction, the tibial tray will not fit correctly on top of the tibia and will overhang at least one side of the tibia.
Conventional tibial prostheses include a tibial tray with a tibial stem. In many tibial prostheses, the stem is fixed relative to the tibial tray. A few commercially available tibial prostheses include either a nut and bolt or a bushing adjoining the tibial tray and tibial stem. These bushings extend deep into the patient's tibia, requiring a large amount of a patient's natural bone to be removed in order to implant the prosthesis. The removal of large amounts of otherwise healthy bone tissue impedes the healing process and promotes movement of the prosthesis within the knee joint.